Over the years, various retaining devices have been developed for safely securing power driven sockets to the rotating anvils of pneumatic air guns or power drives. I have received three patents in this area including U.S. Pat. No. 4,266,453 which issued in 1981 and is entitled “Socket Retaining Ring” (the “1981 patent”), U.S. Pat. No. 4,583,430 which issued in 1986 and is entitled “Metal Shielded Retaining Ring” (the “1986 patent”), and U.S. Pat. No. 6,076,436 which issued in 2000 and is entitled “Retaining Device With Metal Insert” (the “2000 patent”). The disclosures of my foregoing patents are hereby incorporated by reference as if fully set forth herein.
Prior to the 1981 patent, power driven sockets were usually secured to the anvil of a power drive using a metal pin inserted through the bores of the socket aligned with the through-hole of the anvil. In an effort to keep the pin in place, a rubber O-ring was then installed around the periphery of the socket within an annular groove intersecting and covering the aligned bores.
The most dangerous aspect of this prior art was that workmen would often use the large impact tools by only inserting the pin without using the O-ring. Since the O-ring was separate from the pin, the O-ring could easily get lost, neglected or forgotten. Injury could occur during use when the metal pins were violently dislodged by centrifugal force as a result of a defective O-ring or the lack of the O-ring.
In addition, normal usage of the tool would cause wear and tear of the inner surface of the socket, causing the socket to fit less tightly onto the square end of the anvil. During operation, the worn-out socket would rotate relative to the anvil, creating a “scissors-like” action. This “scissors-like” movement applied a shearing force at two places between the inner surface of the socket and the anvil: 1) the first juxtaposition defined by the alignment of the first bore of the socket with the first end of the through-hole of the anvil; and 2) the second juxtaposition defined by the alignment of the second bore of the socket with the second end of the through-hole of the anvil. This shearing force occasionally caused the metal pin to be jammed in the bores of the socket, creating a major inconvenience as workers would have to drill out the lodged metal pins.
The 1981 patent sought to remedy these problems by providing the O-ring and pin as a single, integral piece made of an elastomeric material, e.g. polyurethane. FIG. 1 is a cutaway perspective view of a power drive 5 having an anvil 80. As further shown in FIG. 1, a socket 90 is secured to the anvil with an integral retaining ring 7 as disclosed in the 1981 patent is used to secure the socket 90 to the anvil 80.
The integral unit of the 1981 patent solved the problems caused by separate pieces. As a single unit, a worker could not use the pin without the O-ring, nor the O-ring without the pin. Furthermore, since the pin consisted of the same elastomeric material as the O-ring, workers no longer had to struggle with removing metal pins that were jammed within the bores of the anvil or socket.
However, due to ordinary wear and tear of the socket's drive hole, rotational movement of the socket 90 relative to the anvil 80 would still eventually occur as a part of normal use. The socket's drive hole tends to deform over time because the socket is usually made softer than the anvil so that the tool's life is extended. This rotational movement would occasionally result in the shearing of the retaining ring's elastomeric pin at the two juxtapositions between the anvil 80 and the socket 90.
The 1986 patent improved upon the 1981 patent by encapsulating a metal sleeve into a far a portion of the elastomeric pin. The 1986 patent teaches placing a metal sleeve at a far end of the pin adjacent to the second juxtaposition, which is the juxtaposition furthest away from the base of the pin. Using the metal sleeve improved the safety of the completely polyurethane retaining device disclosed in the 1981 patent. However, since the metal sleeve was hollow, it sometimes could not withstand an especially strong shearing force. In such case, the shearing force could crush or shatter the metal sleeve, destroying the safety of the ring as well as making it very difficult to remove.
The encapsulated steel sleeve of the 1986 patent included an axial through hole so that it was captured between the pin's base and the pin's far end. This was necessary because the steel insert was subjected to a fair amount of centrifugal force due to its relatively great mass being located off axis and thereby being rotated around the axis of the drive's anvil.
The encapsulated steel sleeve of the 1986 patent provided enhanced safety for the operator, but it often became crushed at the far juxtaposition between the anvil 80 and the socket 90 and the operator had to drill it out to remove the socket 90.
The 2000 patent sought to improve on the 1981 and 1986 patents by providing a short pin comprised of an elastomeric base and a steel pin. Unlike the retaining rings that came before it, the steel pin of the retaining ring disclosed in the 2000 patent only extended into the near juxtaposition between the socket 90 and the anvil 80. The short pin device was easier to install, but it did not do well in the marketplace because the operators continued to prefer retaining rings with long pins that passed through both juxtapositions. Moreover, when used with worn sockets, the steel pin of the short pin device fragmented within the juxtaposition and needed to be drilled out.
Being subject to corrosion, the steel pins of the prior devices required additional expense to provide corrosion resistance through heat treating, or plating, or both.
Finally, because the sockets secured by the prior art pins are generally manufactured from a softer steel than the anvil, the interior of the socket's drive aperture can become oversized relative to the anvil's exterior. In such case, the resulting slop may permit the socket to twist somewhat relative to the anvil, thereby shearing the pin, regardless of whether the pin is elastomeric or steel. The worn socket, now free to spin off axis as well, can be thrown at high speed and result in an unfortunate injury to the operator or nearby co-workers. The prior art retaining rings have done little to provide the operator with a definitive visual indication of the socket's suitability for continued use.
There remains a need, therefore, for a long-pin retaining device that eliminates the need for a through hole, that reduces if not eliminates the need to drill out a metal pin in order to remove the socket from the anvil, that does not require expensive corrosion resistance processing, and that provides definitive visual feedback on the socket's suitability for continued use. There also remains a need for a holding pin that does not fail, when crushed, if the operator continues to use a worn socket.